Coiled tubing drilling offers the advantages of reduced time and costs associated with conventional drilling operations that utilize segmented pipe. These advantages include reduced pipe handling time, reduced pipe joint makeup time, and reduced leakage risks.
When coiled tubing drilling is utilized, however, conventional drilling may still be required to drill surface holes due to the lack of bit weight at the surface with coiled tubing drilling. A separate conventional drilling rig is then required to drill a surface hole, place surface casing, cement, and then drill to deeper depths. Thus, hybrid rigs exist that can perform both conventional drilling and coiled tubing drilling.
Hybrid rigs, however, are often utilized in extremely cold environments, such as Alaska. These rigs typically feature a fixed coiled-tubing-reel location, which is cumbersome and difficult to position and operate, particularly in extremely cold environments. Moreover, the entire coiled tubing unit (e.g., reel and injector) is exposed to the cold environment, and can be subject to freeze-up or other weather-induced failure.
One recent advance in the field of coiled tubing rigs is discussed in co-pending U.S. patent application Ser. No. 11/847,437, filed Aug. 30, 2007. That document discloses an apparatus including a mobile trailer, a coiled tubing unit coupled to the mobile trailer, and an enclosure surrounding the coiled tubing unit, which coiled tubing unit may include a coiled tubing reel and a coiled tubing injector. The reel and the injector may be positionally fixed relative to one another and collectively move relative to the mobile trailer as an integral unit.
Additionally, the number and availability of hybrid rigs is low. Major modification or re-design of existing rigs configured for drilling with segmented pipe is typically required to add the capability to drill with coiled tubing. This modification or re-design of existing rigs is expensive and takes a long time. Thus, there remains a need for improved coiled tubing rig equipment and drilling methods.